CN105425330A - Wave-front correction structure based on volume holographic device - Google Patents

Abstract

The invention discloses a wave-front correction structure based on a volume holographic device. The wave-front correction structure comprises a first volume Bragg grating (2), and incident light (1) satisfies a Bragg condition and is shot from the front surface of the first volume Bragg grating (2) and diffracted from the rear surface of the first volume Bragg grating (2). The wave-front correction structure based on the volume holographic device is simple, and can directly correct high-frequency phase distortion of beams at the near field of the beams.

Description

Based on the wavefront correction structure of volume holographic device

Technical field

The present invention relates to wavefront correction technical field, particularly a kind of wavefront correction structure based on volume holographic device.

Background technology

The focal spot characteristic of high-power laser beam affects one of its key factor in the application of high power laser light field.Focal spot characteristic depends primarily on the Beam Wave-Front PHASE DISTRIBUTION before focusing, wherein the main lobe of low frequency phase distortion major decision focal spot, the secondary lobe of medium-high frequency phase distortion major decision focal spot.The medium-high frequency phase distortion of high power laser light in transmitting procedure even likely causes Small-scale Self-focusing effect thus causes the destruction of optical component.Up to the present, the wavefront correction of low frequency mainly utilizes distorting lens to correct, the phase distortion of high frequency can utilize traditional spatial pinhole filter by its filtering, and the phase distortion of intermediate frequency can not correct with distorting lens, do not suppress completely by spatial filtering aperture again, the present invention therefore.

Summary of the invention

The object of the invention is to provide a kind of wavefront correction structure based on volume holographic device, and its structure is simple, can realize the phase distortion of light beam medium-high frequency and directly realize in the near field of light beam correcting.

Based on the problems referred to above, technical scheme provided by the invention is:

Based on the wavefront correction structure of volume holographic device, comprise the first Volume Bragg grating, it is incident and from the rear surface diffraction bright dipping of described first Volume Bragg grating from described first Volume Bragg grating front surface that incident light meets Bragg condition.

Further, also comprise the second Volume Bragg grating, described second Volume Bragg grating is arranged on the diffraction light side of described first Volume Bragg grating outgoing, the diffraction light of described first Volume Bragg grating outgoing is from described second Volume Bragg grating front surface incidence and from described second Volume Bragg grating rear surface diffraction bright dipping, the grating vector of described first Volume Bragg grating and described second Volume Bragg grating is mutually orthogonal.

Further, described first Volume Bragg grating and described second Volume Bragg grating are transmission-type grating, and described first Volume Bragg grating and described second Volume Bragg grating are phase grating.

Further, described first Volume Bragg grating and described second Volume Bragg grating all adopt photic temperature-sensitive refractive index glass to make.

Further, described photic temperature-sensitive refractive index glass is the silicate glass doped with cerium, silver and fluorine.

Further, the grid line adjustable angle of described first Volume Bragg grating and described second Volume Bragg grating.

Principle of work of the present invention is: when incident light Volume Bragg grating incident with Bragg condition, corresponding secondary lobe is there is in the medium-high frequency phase distortion in light beam during spectrum light beam can be made to distribute, utilize the angle selectivity characteristic of Volume Bragg grating, the secondary lobe that these phase distortions bring effectively can be reduced, thus the wavefront properties of diffraction light is optimized.

Compared with prior art, advantage of the present invention is:

1, technical scheme of the present invention is adopted, incident light is incident to Volume Bragg grating with Bragg condition, utilize the medium-high frequency phase distortion in the angle selectivity characteristic reduction light beam of Volume Bragg grating, thus realize correcting in the near field of light beam to the medium-high frequency phase distortion of light beam, this wavefront correction structure, structure is simple, can avoid the Pinhole closure of pin hole spatial filter in high power laser light application;

2, adopt the further technical scheme of the present invention, Volume Bragg grating prepared by photic temperature-sensitive refractive index glass, Laser-induced damage threshold is high, can bear 10J/cm ²energy density;

3, adopt the further technical scheme of the present invention, the wavefront correction ability of Volume Bragg grating can be adjusted according to tuning grating structural parameter, i.e. the diffraction efficiency of different angular spectrum.

Accompanying drawing explanation

In order to be illustrated more clearly in the technical scheme of the embodiment of the present invention, below the accompanying drawing used required in describing embodiment is briefly described, apparently, accompanying drawing in the following describes is only some embodiments of the present invention, for those of ordinary skill in the art, under the prerequisite not paying creative work, other accompanying drawing can also be obtained according to these accompanying drawings.

Fig. 1 is the structural representation of the wavefront correction constructive embodiment that the present invention is based on volume holographic device;

Fig. 2 is wavefront comparison diagram before and after the incident Volume Bragg grating of actual light beam, grating angle selects width to be 1.30mrad, wherein (a) and (b) represents the wavefront distribution of incipient beam of light, (c) and (d) represent light beam receive phase-plate modulation after wavefront distribution, (e) and (f) represents the distribution of the wavefront after two blocks of gratings;

Fig. 3 is the far-field distribution comparison diagram of actual light beam, wherein schemes the far-field distribution that (a), (b), (c) represent incipient beam of light, modulated beam of light and diffracted beam respectively;

Wherein:

1, incident light; 2, the first Volume Bragg grating; 3, the second Volume Bragg grating.

Embodiment

Below in conjunction with specific embodiment, such scheme is described further.Should be understood that these embodiments are not limited to for illustration of the present invention limit the scope of the invention.The implementation condition adopted in embodiment can do further adjustment according to the condition of concrete producer, and not marked implementation condition is generally the condition in normal experiment.

See Fig. 1, for the structural representation of the embodiment of the present invention, a kind of wavefront correction structure based on volume holographic device is provided, it comprises the first Volume Bragg grating 2, incident light 1 after the first Volume Bragg grating 2 front surface incidence in the rear surface diffraction bright dipping of the first Volume Bragg grating 2, when incident light 1 first Volume Bragg grating 2 incident with Bragg condition, the angle selectivity characteristic of Volume Bragg grating, the secondary lobe that the medium-high frequency phase distortion in light beam can be brought effectively reduces, thus the wavefront properties of diffraction light is optimized.

In order to optimize implementation result of the present invention further, also comprise the second Volume Bragg grating 3, this second Volume Bragg grating 3 is arranged on the diffraction light side of the first Volume Bragg grating 2 outgoing, the diffraction light of the first Volume Bragg grating 2 outgoing is from the front surface of the second Volume Bragg grating 3 is incident and from the second Volume Bragg grating 3 rear surface diffraction bright dipping, the grating vector of the first Volume Bragg grating 2 and the second Volume Bragg grating 3 is mutually orthogonal.

Above-mentioned first Volume Bragg grating 2 and the second Volume Bragg grating 3 are transmission-type grating, and are phase grating, and the first Volume Bragg grating 2 and the second Volume Bragg grating 3 are uniform period body grating.

First Volume Bragg grating 2 and the second Volume Bragg grating 3 can also be two knockdown Volume Bragg gratings of block, and namely each Volume Bragg grating is formed by the daughter grating combination that two pieces of grid lines are orthogonal, and the grating thickness of two blocks of daughter gratings or cycle can be different.

First Volume Bragg grating 2 and the second Volume Bragg grating 3 are prepared from by photic temperature-sensitive refractive index glass, this photic temperature-sensitive refractive index glass is the silicate glass doped with cerium, silver and fluorine, common holographic material (halogenide silver photosensitive emulsion, dichromatism gel, photoresist etc.) can shrink in heat treatment process, also very sensitive for humidity, high power laser light irradiation can not be born.

Bragg grating has outstanding Prague selective power, i.e. angular selectivity and spectral selectivity, and higher diffraction efficiency and laser damage threshold, the parameters such as its incident angle, angle of diffraction, centre wavelength, angle (spectrum) selectivity, can regulate by changing the grating structural parameters such as grating thickness, refractive index modulation degree, screen periods, grating vector pitch angle.

According to classical Kogelnik coupled wave theory, the diffraction efficiency of the phase type Volume Bragg grating of absorption is had to be:

$\mathrm{\η}=\exp (-\frac{2\mathrm{\α}d}{c_R})\×\frac{{\sin }^2(v^2+{\mathrm{\ξ}}^2)}{1+{\mathrm{\ξ}}^2/v^2}$

Wherein:

$v=\frac{{\mathrm{\πn}}_{1}d}{\mathrm{\λ}\sqrt{cos\mathrm{\θ}(\cos \mathrm{\θ}-Kcos\mathrm{\φ}/\mathrm{\β})}}$

$\mathrm{\ξ}=\frac{\mathrm{\Δ}\mathrm{\θ}Kdsin(\mathrm{\φ}-{\mathrm{\θ}}_0)}{2(\cos \mathrm{\θ}-K\cos \mathrm{\φ}/\mathrm{\β})}$

In formula: K represents grating vector, be inversely proportional to screen periods, d, n ₁represent grating thickness respectively with φ, refractive index modulation degree and grating vector pitch angle, α is absorption coefficient, and β represents the wave vector of incident light, θ ₀represent the Bragg angle of grating, Δ θ represents the angular metric departing from Bragg condition.The design of Volume Bragg grating structural parameters can be instructed, to realize required diffraction bandwidth by above-mentioned diffraction formula.

See Fig. 2, it is wavefront comparison diagram before and after the incident Volume Bragg grating of actual light beam, grating angle selects width to be 1.30mrad, wherein Fig. 2 (a) and (b) represent the wavefront distribution of incipient beam of light, Fig. 2 (c) and (d) represent light beam receive phase-plate modulation after wavefront distribution, Fig. 2 (e) and (f) represent the distribution of the wavefront after two blocks of gratings.Visible wavefront distortion after optical grating diffraction has obvious suppression.Corresponding PV value and RMS value as shown in table 1.

PV value before and after the incident Volume Bragg grating of table 1 actual light beam and RMS value

	Original beam	Modulated beam of light	Diffracted beam
				PV value	0.348λ	2.075λ	0.209λ
RMS value	0.077λ	0.207λ	0.041λ

See Fig. 3, be the far-field distribution comparison diagram of actual light beam, wherein Fig. 3 (a), (b), (c) represent the far-field distribution of incipient beam of light, modulated beam of light and diffracted beam respectively.The secondary lobe place maximal value of original beam is 0.11, after phase-plate modulation, modulated beam of light far-field distribution has obvious secondary lobe to occur, maximal value is 0.14, after optical grating diffraction, secondary lobe maximal value reduces to 0.04, corresponding Si Telieer ratio and as shown in table 2 around power, and this illustrates that the far-field characteristic of light beam and focus characteristics are improved.

Si Telieer ratio before and after the incident Volume Bragg grating of table 2 actual light beam and around power

Above-mentioned example, only for technical conceive of the present invention and feature are described, its object is to person skilled in the art can be understood content of the present invention and implement according to this, can not limit the scope of the invention with this.All equivalent transformations of doing according to Spirit Essence of the present invention or modification, all should be encompassed within protection scope of the present invention.

Claims (6)

1. based on the wavefront correction structure of volume holographic device, it is characterized in that: comprise the first Volume Bragg grating (2), it is incident and from the rear surface diffraction bright dipping of described first Volume Bragg grating (2) from described first Volume Bragg grating (2) front surface that incident light (1) meets Bragg condition.

2. the wavefront correction structure based on volume holographic device according to claim 1, it is characterized in that: also comprise the second Volume Bragg grating (3), described second Volume Bragg grating (3) is arranged on the diffraction light side of described first Volume Bragg grating (2) outgoing, the diffraction light of described first Volume Bragg grating (2) outgoing is from described second Volume Bragg grating (3) front surface incidence and from described second Volume Bragg grating (3) rear surface diffraction bright dipping, described first Volume Bragg grating (2) is mutually orthogonal with the grating vector of described second Volume Bragg grating (3).

3. the wavefront correction structure based on volume holographic device according to claim 2, it is characterized in that: described first Volume Bragg grating (2) and described second Volume Bragg grating (3) are transmission-type grating, and described first Volume Bragg grating (2) and described second Volume Bragg grating (3) are phase grating.

4. the wavefront correction structure based on volume holographic device according to claim 3, is characterized in that: described first Volume Bragg grating (2) and described second Volume Bragg grating (3) all adopt photic temperature-sensitive refractive index glass to make.

5. the wavefront correction structure based on volume holographic device according to claim 4, is characterized in that: described photic temperature-sensitive refractive index glass is the silicate glass doped with cerium, silver and fluorine.

6. the wavefront correction structure based on volume holographic device according to claim 5, is characterized in that: the grid line adjustable angle of described first Volume Bragg grating (2) and described second Volume Bragg grating (3).